Method and apparatus for extending calls to internal switch extensions out to external network endpoints

ABSTRACT

A private branch exchange (PBX) or other communication system switch processes a call to determine if an identifier associated with the call has a corresponding entry in a stored list of external endpoints registered with the switch. The switch directs the call to an external port of the switch for delivery to a given one of the external endpoints if the identifier associated with the call has a corresponding entry in the stored list of external endpoints registered with the switch. The given external endpoint does not have a fixed external port assignment in the switch. Instead, the switch dynamically selects from a set of external ports an available external port over which the call is directed to the given external endpoint. The dynamic selection of the available external port may be implemented using an automatic route selection (ARS) algorithm. The switch in an illustrative embodiment directs the call to an external port of the switch via a loop-back arrangement implemented between port cards of the switch, e.g., a loop-back trunk between an output port associated with a first port card of the switch and an input port associated with a second port card of the switch. Advantageously, the registered external endpoint is treated by the switch as if it were an internal extension serviced by the switch, such that desirable switch features may thereby be made available to the external endpoint.

RELATED APPLICATION

[0001] The present invention is related to an invention described inU.S. Patent Application Attorney Docket No. 500022-A-01-US (Milton),filed concurrently herewith in the name of inventor Stephen M. Miltonand entitled “Method and Apparatus for Treating Externally-OriginatedCalls as Coming From Internal Switch Extensions,” which is incorporatedby reference herein.

FIELD OF THE INVENTION

[0002] The invention relates generally to call processing incommunication systems, and more particularly to systems in which callsor other communications are directed by a switch to or from wired orwireless telephones or other types of user terminals.

BACKGROUND OF THE INVENTION

[0003] Conventional communication system switches, such as privatebranch exchanges (PBXs) and other premises-based telephone switches,generally support a wide variety of useful features, such as bridgedcall appearances, hunt groups, call forwarding, navigable directories,multi-call conferencing, etc. However, these and other switch-basedfeatures are typically provided only to those user terminals thatrepresent internal extensions within the premises serviced by theswitch. As a result, a user terminal associated with an external networkis generally unable to avail itself of the full set of featuressupported by the switch.

[0004] By way of example, a mobile telephone or other mobile devicerepresenting a given external endpoint of the system generally cannot betreated as an internal extension of a conventional switch. A calldirected from an internal extension of the switch to the given endpointtherefore must be processed as any other call to an endpoint of anexternal network, even if the given external endpoint is a device knownto be associated with a user of an internal extension of the switch.

[0005] It is known in the art to implement call forwarding routines thatwill allow a call directed from one internal extension to another to beforwarded to a designated mobile telephone or other endpoint of anexternal network. However, in conventional call forwarding, thedesignated mobile telephone is not treated as if it were an internalextension serviced by the switch, and is generally unable to access manydesirable features of the switch. Conventional switches are thus unableto extend switch-based features to such a call in an efficient andcost-effective manner.

[0006] A need therefore exists for call processing techniques that allowmobile telephones and other external system endpoints to accesspremises-based communication switch features in a manner similar to aninternal extension serviced by the switch.

SUMMARY OF THE INVENTION

[0007] The present invention provides methods and apparatus forextending calls directed to internal switch extensions out to externalnetworks, so as to allow a mobile telephone or other external endpointto be treated as if it were an internal extension serviced by theswitch.

[0008] In accordance with one aspect of the invention, a private branchexchange (PBX) or other communication system switch processes a call todetermine if an identifier associated with the call has a correspondingentry in a stored list of external endpoints registered with the switch.The switch directs the call to an external port of the switch fordelivery to a given one of the external endpoints if the identifierassociated with the call has a corresponding entry in the stored list ofexternal endpoints registered with the switch. The given externalendpoint in an illustrative embodiment of the invention does not have afixed external port assignment in the switch. Instead, the switchdynamically selects from a set of external ports an available externalport over which the call is directed to the given external endpoint. Thedynamic selection of the available external port may be implementedusing an automatic route selection (ARS) algorithm.

[0009] In an illustrative embodiment of the invention, the switchdirects the call to an external port of the switch via a loop-backarrangement implemented between port cards of the switch, e.g., aloop-back trunk between an output port associated with a first port cardof the switch and an input port associated with a second port card ofthe switch. In other embodiments, the loop-back arrangement may beeliminated and the call routed directly to an external port of theswitch after application of the ARS algorithm.

[0010] Advantageously, the invention allows a mobile telephone or otherexternal endpoint to be treated as if it were an actual internalextension serviced by the switch. This in turn allows a given externalendpoint to access at least a subset of the desirable call processingfeatures provided by the switch, and thereby overcomes one or more ofthe above-described problems associated with conventional techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 shows an exemplary communication system in which theinvention is implemented.

[0012]FIG. 2 is a block diagram showing one possible implementation of aswitch of the FIG. 2 system.

[0013]FIG. 3 is a flow diagram illustrating call processing operationsperformed by the switch in the system of FIG. 1 in accordance with thetechniques of the invention.

[0014]FIG. 4 is a diagram illustrating the manner in which a call isdirected by the switch to a registered external endpoint in accordancewith the techniques of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0015] The invention will be illustrated below in conjunction with anexemplary communication system. Although well suited for use with, e.g.,a system having a private branch exchange (PBX) or other similar callprocessing switch, the invention is not limited to use with anyparticular type of communication system switch or configuration ofsystem elements. Those skilled in the art will recognize that thedisclosed techniques may be used in any communication application inwhich it is desirable to provide improved control of calls directed toexternal endpoints from internal extensions of a PBX or othercommunication system switch. The term “call” as used herein is intendedto include not only telephone calls but also non-telephoniccommunications such as data transmissions, voice-over-IP, facsimile,etc.

[0016]FIG. 1 shows an exemplary communication system 100 in which theinvention is implemented. The system 100 includes a switch 102 whichserves a premises 104 having a number of terminals 106-1, 106-2, . . .106-N. Each of the terminals 106-1, 106-2, . . . 106-N corresponds toone of a set of internal extensions Ext1, Ext2, . . . ExtN as shown.These extensions are referred to herein as “internal” in that they areextensions within the premises 104 that are directly serviced by theswitch. More particularly, these extensions correspond to conventionalterminal endpoints serviced by the switch, and the switch can directincoming calls to and receive outgoing calls from these extensions in aconventional manner.

[0017] The term “switch” as used herein should be understood to includea PBX, an enterprise switch, or other type of telecommunications systemswitch, as well as other types of processor-based communication controldevices such as servers, computers, adjuncts, etc.

[0018] By way of example, the switch 102 in the illustrative embodimentmay be implemented as an otherwise conventional DEFINITY® EnterpriseCommunication Service (ECS) communication system switch available fromAvaya Inc. of Basking Ridge, N.J., USA. Other types of known switchesmay be used. The conventional aspects of such switches are well known inthe art and therefore not described in detail herein.

[0019] The terminals 106 may be wired desktop telephone terminals or anyother type of terminals capable of communicating with the switch 102.The word “terminal” as used herein should therefore be understood toinclude not only wired or wireless desktop telephone terminals, but alsoother types of processor-based communication devices, including but notlimited to mobile telephones, personal computers, personal digitalassistants (PDAs), etc.

[0020] The switch 102 is also coupled via one or more trunk lines 110 toa public switched telephone network (PSTN) 112. The trunk lines 110carry incoming calls from the PSTN 112 to the switch 102 for processing,and carry outgoing calls from the switch 102 to the PSTN 112. The PSTN112 is coupled to one or more wireless networks 114, which haveassociated therewith terminals 116-1, 116-2, . . . 116-K.

[0021] It should be noted that the invention does not require anyparticular type of information transport medium between switch 102 andterminals 116, i.e., the invention may be implemented with any desiredtype of transport medium as well as combinations of different types oftransport media. The one or more wireless networks 114 may be wirelesscellular systems of a type well known in the art.

[0022] Each of the terminals 116-1, 116-2, . . . 116-K represents anexternal terminal not corresponding to any internal extension of theswitch 102. These terminals are referred to as “external” in that theyare not directly supported as terminal endpoints by the switch 102. Likethe terminals 106, the terminals 116 may be wired or wireless desksets,mobile telephones, personal computers, PDAs, etc. The terminals 116 arean example of devices more generally referred to herein as “externalendpoints.”

[0023] Although shown as being connected to the wireless network(s) 114in FIG. 1, one or more of the external terminals 116 could instead beconnected directly to the PSTN 112. More generally, the presentinvention can be implemented using any desired type of external endpointand network connection.

[0024] As will be described in greater detail below, the presentinvention in accordance with one aspect thereof configures the switch102 such that one or more of the external terminals 116 are treatedsubstantially as internal switch extensions. Advantageously, this allowsa given external terminal to access at least a subset of the desirablecall processing features provided by the switch 102.

[0025] It should be emphasized that the configuration of the switch,user terminals and other elements as shown in FIG. 1 is for purposes ofillustration only, and should not be construed as limiting the inventionto any particular arrangement of elements.

[0026]FIG. 2 shows a more detailed view of one possible implementationof the switch 102 in the system of FIG. 1. The switch 102 in thisimplementation includes a processor 200, a memory 202, a database 204,one or more interfaces 206, a switch fabric 208, and a set of servicecircuits 210. The processor 200 may be implemented as a centralprocessing unit (CPU), microprocessor, application-specific integratedcircuit (ASIC) or other type of digital data processor, as well asvarious portions or combinations of such elements. The memory 202 may bea random access memory (RAM), a read-only memory (ROM) or combinationsof these and other types of electronic memory devices.

[0027] The processor 200 operating in conjunction with the memory 202executes one or more software programs for providing feature processingand other functions within the switch 102. The manner in which suchfunctions are made accessible to one or more of the external terminals116 will be described in greater detail below in conjunction with theflow diagram of FIG. 3. Such programs may be stored in memory 202 oranother storage device accessible to the switch 102 and executed byprocessor 200 in a conventional manner.

[0028] The database 204 may be, e.g., an optical or magnetic disk-basedstorage device, or other conventional storage device associated with orotherwise accessible to the switch 102. The database 204 may be used tostore, e.g., feature assignments to particular feature buttons or codes,directory number assignments to corresponding call appearances or directfacility termination keys, access restrictions, and other knownadministrative information regarding the configuration of the system100, as well as other types of information.

[0029] The service circuits 210 may include tone generators,announcement circuits, etc. These circuits and the interfaces 206 arecontrolled by processor 200 in implementing call processing functions inthe switch 102.

[0030] The switch 102 may include additional elements which are omittedfrom FIG. 2 for simplicity and clarity of illustration. For example, theswitch may include a port card for each type of user terminal associatedtherewith. In addition, it will be appreciated by those skilled in theart that the switch 102 may be configured to support multiple userterminals of different types, e.g., wired deskset terminals, wirelessdeskset terminals, personal computers, video telephones or otheradvanced terminals, etc.

[0031] Also associated with the switch 102 may be an administratorterminal (not shown) which is used to program the operation of theswitch 102 during a system administration, e.g., an initial set-up andconfiguration of the system or a subsequent system-level or user-levelreconfiguration.

[0032] Other devices not shown in the figures may be associated with theswitch 102, such as an adjunct feature server. Such an adjunct may bephysically incorporated within the switch, and may be partially orcompletely implemented using other switch elements such as processor 200and memory 202.

[0033]FIG. 3 is a flow diagram illustrating the manner in which anoutgoing call may be directed by the switch 102 to a given one of theexternal terminals 116. In accordance with the invention, the switch 102is configured such that the given external terminal to which theoutgoing call is directed is treated as an internal switch extension.

[0034] In step 300, a mobile telephone or other external endpoint isregistered with the switch 102. This registration step can beimplemented by a system administrator, or through another suitablemanual or automated technique. As a result of this registration process,the switch in step 302 stores an identifier of the external endpoint ina stored list of external terminals or other endpoints registered withthe switch. The entry may include, e.g., the identifier associated withthe external endpoint, a corresponding internal extension notcorresponding to any internal terminal or other endpoint directlyserviced by the switch, an internal extension of an associated internalterminal, and/or other information.

[0035] A call is placed to the registered external endpoint from aninternal switch extension in step 304. The internal switch extensioncorresponds to an internal terminal or endpoint directly serviced by theswitch. For example, the call may originate from one of the terminals106 of FIG. 1 within premises 104 and corresponding to a particular oneof the above-noted internal switch extensions Ext1, Ext2, . . . ExtN.

[0036] The call referred to in step 304 may be a call originated bydirectly dialing from one of the internal extensions a number associatedwith the external endpoint. As another example, the call may be a callmade from one internal extension to another internal extension, wherethe other internal extension has the external endpoint associatedtherewith in a manner similar to that described in conjunction with theabove-noted registration process. Further details regarding theprocessing of the latter type of call will be described below inconjunction with FIG. 4.

[0037] The switch in step 306 determines if the external endpointassociated with outgoing call has been registered with the switch in themanner previously described. For example, the switch may attempt to mapan identifier extracted from the outgoing call to an entry in theabove-noted stored list of endpoints. The identifier may be, e.g., thecalled number of the outgoing call, and may be made apparent to theswitch through well-known conventional techniques such as automaticnumber identification (ANI). Other types of identifiers can also beused. For example, particular identifiers may be assigned to knownexternal terminals or other external endpoints associated with users ofthe internal extension terminals 106, e.g., by a system administrator orotherwise, and stored in a tabular form in the memory 202 or database204 using conventional techniques.

[0038] The term “stored list” as used herein should be understood toinclude any set of information stored in a memory or other storagedevice accessible to the switch. The invention does not require that theinformation be stored in any particular format, e.g., a tabular format,and numerous suitable storage formats will be readily apparent to thoseskilled in the art.

[0039] As indicated above, once the identifier associated with theoutgoing call has been extracted or otherwise made apparent to theswitch 102, an attempt is made to map the identifier to a particularentry on the above-noted stored list via table look-up or other suitabletechnique. If the extracted identifier has a corresponding entry on thestored list, the switch places the call over an external trunk via aloop-back trunk, as indicated in step 306. This illustrative techniquefor placement of the outgoing call allows the switch to treat the callas being directed to an internal extension, as indicated in step 308,and will be described in greater detail below in conjunction with FIG.4. If the switch determines that a particular outgoing call does nothave an identifier with a corresponding entry on the stored list ofidentifiers, the call is processed in a conventional manner as any otherexternally-directed call.

[0040] The term “map” as used herein is intended to be construed broadlyto include any technique for determining if a given identifier has acorresponding entry on a stored list.

[0041] A station display or other information presented to the calloriginator extension may be configured to indicate that an outgoing callto a registered external endpoint was received at an internal extensionof the switch.

[0042] It should be noted that it is possible to associate with each ofthe stored external endpoint identifiers a corresponding actual internalextension, such as extensions designated as N+1, N+2, etc. As indicatedabove, such extensions may be assigned to registered external endpointsand entered in the stored list. Calls directed to a given externalterminal are then processed as if they were directed to thecorresponding assigned internal extension. However, the switch canprovide the above-described processing without assignment of an actualinternal extension to a given external terminal.

[0043]FIG. 4 illustrates the manner in which a call from an internalextension may be directed by the switch 102 to a registered externalendpoint via the loop-back trunk referred to in step 306 of FIG. 3. Theswitch 102 as shown in FIG. 4 includes port cards denoted A, B, C and D,and call processing elements 400, 402 and 404.

[0044] Port card A is coupled to a given one of the internal terminals106-i of system 100. Port cards B and C are each coupled to a loop-backtrunk 410 as shown. Port card D is coupled to an external trunk 412 thatrepresents one of the trunk lines 110 of FIG. 1 and provides aconnection via PSTN 112 and wireless network(s) 114 to a given externalendpoint in the form of a mobile telephone 116-j. Port cards C and D arecoupled via a connection 415 internal to the switch 102 as shown. Theports cards A, B, C and D may be conventional switch port cards of atype well known in the art. For example, port card A may be aconventional digital board card, while port cards B, C and D may beconventional UDS1 cards of a type more specifically known as TN464F orTN2464 and physically configured for 32 channel operation. Port cards Band C are preferably cabled in a loop-back arrangement with transmitleads connected to receive leads.

[0045] The terms “trunk” and “trunk line” as used herein should beunderstood to include POTS telephone lines, integrated services digitalnetwork (ISDN) lines, T1 lines or various portions or combinations ofthese and other types of transport media.

[0046] The switch 102 in this illustrative example has two externalendpoints registered therewith, denoted as Xmobile 1 and Xmobile 2 inthe figure. Each of these registered external endpoints is associatedwith a corresponding one of the processing elements 402 and 404. Theprocessing elements 402 and 404 may be viewed as comprising portions ofthe above-noted stored list associated with the respective externalendpoints Xmobile 1 and Xmobile 2, and may also include correspondingsoftware code required to implement at least a portion of thepreviously-described mapping process.

[0047] It is assumed for purposes of the present example that the sameuser associated with the internal extension terminal 106-i is alsoassociated with the Xmobile 1 external endpoint, and that the Xmobile 1external endpoint is the mobile telephone 116-j shown in the figure. Anentry for the Xmobile 1 external endpoint in the above-noted stored listmay therefore include information specifying the associated internalextension.

[0048] In operation, a call 420 originated by one of the internalextensions other than that corresponding to terminal 106-i is processedby processing element 400 in accordance with first and second callappearances, denoted CA1 and CA2. Elements 400, 402 and 404 as shown inFIG. 4 implement a bridging of analog stations corresponding to Xmobile1 and Xmobile 2 to a multi-function digital deskset corresponding toterminal 106-i. In this particular bridging arrangement, a separateanalog station is bridged to each of two call appearances on the digitaldeskset. The call appearances CA1 and CA2 are thus both associated withthe terminal 106-i. When a call is delivered to either call appearanceit will also be delivered to the corresponding Xmobile endpoint. Thecall to that Xmobile endpoint then proceeds out via the loop-back trunk410.

[0049] More particularly, FIG. 4 illustrates a call associated with thefirst call appearance CA1 proceeding in the manner indicated viaprocessing element 402 and port card B to the loop-back trunk 410. Fromthe loop-back trunk 410, CA1 is directed to port card C and then viaconnection 415 to port card D and the external trunk 412. The connectionof the call appearance CA1 from external trunk 412 to the Xmobile 1external endpoint 116-j then proceeds in a conventional manner. The call420 in this example may therefore be answered at either the internalterminal 106-i or the external terminal 116-j. If neither of theterminals answer the call, then standard coverage arrangements may takeeffect. As noted previously, the FIG. 4 example may thus be viewed as atype of bridging between the internal terminal 106-i and the externalterminal 116-j. The switch 102 may also be configured to permit a userto dynamically enable or disable the generation of the call appearanceCA1 at the external terminal. Appropriate security codes may be requiredto prevent tampering with this feature.

[0050] It should be emphasized that the particular bridging arrangementof FIG. 4 is shown for illustrative purposes only, and should not beconstrued as limiting the scope of the invention in any way.

[0051] The external terminal 116-j in the FIG. 4 example is not tied toany particular fixed external trunk line. Instead, the call 420 isdirected to that terminal via an otherwise conventional automatic routeselection (ARS) algorithm that dynamically allocates one of a number ofavailable external trunks for use with the call 420. As a moreparticular example, each of the external endpoints registered with theswitch 102 may be associated with a given ISDN-PRI (primary rateinterface) trunk group, such that when a call is to be delivered to aregistered external endpoint, an available trunk line is selected fromthe associated trunk group and the call is routed over that line. Theexternal trunk 412 may thus be viewed as one such selected trunk line.Since there is no fixed port assignment for the external terminal 116-j,this embodiment of the invention provides more efficient allocation ofexternal trunk resources.

[0052] Additional details regarding conventional trunking arrangementsin a PBX or other type of communication system switch utilizable inconjunction with the invention may be found in DEFINITY®ECS, Release 9,Administration for Network Connectivity, Issue 2, Document No.555-233-504, November 2000, which is incorporated by reference herein.

[0053] Although the FIG. 4 example involves a call from one internalextension to another internal extension having an associated externalendpoint, similar arrangements may be used to direct a call from oneinternal extension directly to a registered external endpoint that doesnot have any internal extension associated therewith.

[0054] It should also be noted that the loop-back trunk arrangementillustrated in FIG. 4 may be eliminated in other embodiments of theinvention. In this case, the call 420 may be routed directly to anexternal port of the switch after application of the above-noted ARSalgorithm or other suitable routing technique.

[0055] Advantageously, the invention allows a given external endpoint tobe treated as if it were an internal extension directly serviced by theswitch. The external endpoint may thereby be provided with access tosubstantially all of the desirable switch features that are provided tothe internal extensions.

[0056] As previously noted, the call processing functions describedabove in conjunction with the illustrative embodiment of the inventionmay be implemented in whole or in part in the switch 102, e.g., in callprocessing software thereof utilizing processor 200 and memory 202. Forexample, one or more of the processing elements 400, 402 and 404 of FIG.4 may be implemented using software executed by processor 200 and storedin memory 202. Other suitable combinations of hardware and/or softwaremay be used to implement the call processing functions of the invention.

[0057] It should again be emphasized the above-described embodiment isillustrative only. Alternative embodiments may utilize different switchand terminal configurations, different types of internal and externalendpoints, and different techniques for processing calls directed toterminals or other external endpoints not directly serviced by theswitch.

[0058] By way of example, the invention, although illustrated inconjunction with mobile telephone external endpoints, is also wellsuited for use with external interactive voice response (IVR) unitshaving ISDN interfaces, so as to provide a better level of integrationbetween a PBX or other switch and an external IVR unit. Such IVR unitsare considered a type of external endpoint that may be utilized inconjunction with the invention. As another example, it is possible for asingle external endpoint, such as Xmobile 1 or Xmobile 2 in the FIG. 4embodiment, to support simultaneously two calls sent out over twotrunks. More particularly, it is possible for the switch to beconfigured such that two calls may be directed to a given registeredexternal endpoint using two different trunks, each associated with adifferent external port of the switch. Such an arrangement can beimplemented using a straightforward modification of the above-describedarrangements.

[0059] These and numerous other alternative embodiments within the scopeof the following claims will be apparent to those skilled in the art.

What is claimed is:
 1. A method of processing a call in a communicationsystem switch, the method comprising the steps of: determining if anidentifier associated with the call has a corresponding entry in astored list of external endpoints registered with the switch; anddirecting the call to an external port of the switch for delivery to agiven one of the external endpoints if the identifier associated withthe call has a corresponding entry in the stored list of externalendpoints registered with the switch.
 2. The method of claim 1 whereinthe call is originated at an internal endpoint serviced by the switch.3. The method of claim 1 wherein the call is originated at anoriginating external endpoint.
 4. The method of claim 1 wherein thegiven external endpoint does not have a fixed external port assignmentin the switch.
 5. The method of claim 1 wherein the directing stepfurther comprises dynamically selecting from a set of external ports anavailable external port over which the call is directed to the givenexternal endpoint.
 6. The method of claim 5 wherein the dynamicselection of the available external port is implemented using anautomatic route selection (ARS) algorithm.
 7. The method of claim 1wherein the directing step further comprises directing the call to theexternal port of the switch via a loop-back arrangement implementedbetween port cards of the switch.
 8. The method of claim 7 wherein theloop-back arrangement comprises a loop-back trunk between an output portassociated with a first port card of the switch and an input portassociated with a second port card of the switch.
 9. The method of claim1 wherein the determining step comprises mapping the identifierassociated with the call to the corresponding entry in the stored listof external endpoints registered with the switch.
 10. The method ofclaim 1 wherein the corresponding entry comprises the identifierassociated with the call and an internal extension assigned to anexternal terminal and not associated with any internal endpoint servicedby the switch.
 11. The method of claim 1 wherein the switch isconfigured such that a given one of the external endpoints registeredwith the switch can simultaneously support (i) the call delivered viathe external port, and (ii) at least one additional call delivered viaanother external port of the switch.
 12. The method of claim 1 whereinthe external endpoint comprises a wireless terminal coupled to awireless network external to a premises serviced by the switch.
 13. Themethod of claim 1 wherein the external endpoint comprises a wiredterminal coupled to a wired network external to a premises serviced bythe switch.
 14. The method of claim 1 wherein the external endpointcomprises an external interactive voice response (IVR) unit.
 15. Themethod of claim 1 wherein the switch comprises a private branch exchange(PBX).
 16. The method of claim 1 wherein one or more of the externalendpoints registered with the switch are each bridged to at least oneinternal endpoint serviced by the switch.
 17. A communication systemswitch for use in processing a call, the switch comprising: a memory;and a processor coupled to the memory, the processor being operative todetermine if an identifier associated with the call has a correspondingentry in a stored list of external endpoints registered with the switch,and to direct the call to an external port of the switch for delivery toa given one of the external endpoints if the identifier associated withthe call has a corresponding entry in the stored list of externalendpoints registered with the switch.
 18. The communication systemswitch of claim 17 wherein the switch comprises a private branchexchange (PBX).
 19. An article of manufacture comprising amachine-readable storage medium storing one or more programs for use inprocessing a call in a communication system switch, wherein the one ormore programs when executed implement the steps of: determining if anidentifier associated with the call has a corresponding entry in astored list of external endpoints registered with the switch; anddirecting the call to an external port of the switch for delivery to agiven one of the external endpoints if the identifier associated withthe call has a corresponding entry in the stored list of externalendpoints registered with the switch.